As a kind of heat treatment apparatus which performs a film-forming process for a semiconductor wafer (hereinafter, referred to as “wafer”), there is known a vertical heat treatment apparatus which performs a film-forming process for a plurality of wafers carried in a reaction tube, with the wafers loaded onto a wafer boat which is a substrate supporter. Grooves are formed in sides of supporting columns provided between a ceiling plate and a bottom plate of the wafer boat and each wafer is horizontally supported with its periphery inserted in the grooves of the supporting columns.
Meanwhile, processes of forming a polysilicon film or a polysilicon doped with boron (B) or phosphorus (P) having a thickness of, for example, 1 μm to 2 μm, which is considerably thick from the standpoint of typical semiconductor manufacturing processes, have been studied. In addition, there has been a desire to form a silicon oxide (SiO2) film, a silicon nitride (SiN) film or a carbon film having a thick thickness of, for example, 3000 Å (300 nm) or so. In need of development for the formation of such a thick film, it has been considered that the thick film is applied to a 3D memory using a multilayered stack structure represented by bit-cost scalable (BICS) flash technology, terabit cell array transistor (TCAT) technology or the like. Examples of such a stack structure may include a stack structure having twenty-four (24) layers, each including a polysilicon film having a thickness of 500 Å (50 nm) and a silicon oxide film having a thickness of 500 Å formed thereon; a stack structure having 24 layers, each including a silicon oxide film having a thickness of 500 Å and a silicon nitride film having a thickness of 500 Å formed thereon; and further a stack structure having 24 layers, each including a silicon film having a thickness of 500 Å and a silicon germanium (SiGe) film having a thickness of 500 Å formed thereon.
However, since film forming gas fed into the reaction tube goes around a contact portion between the rear side of the wafer and the grooves, if the film becomes thick, a film is formed on the contact portion. This may result in separation of the film formed on the contact portion when the wafer is drawn (lifted up) out of the wafer boat, which may generate unwanted particles. In addition, when the wafer is drawn out of the wafer boat with the film formed on the contact portion going around the rear side of the wafer, the wafer may not be horizontally loaded in a subsequent process such as lithography (exposure), which may result in misalignment due to the surface of the wafer being out-of-focus. In addition, since the wafer may be adhered to (or integrated with) the wafer boat via the film formed on the contact portion, the wafer may not be drawn out of the wafer boat after film formation.
In the prior art, there is known a technique of forming a polysilicon film, in which a boat loaded with a wafer is taken out of a reaction chamber during film formation and a film-forming process is resumed after floating the wafer from the boat. However, suspension of the film formation increases film formation time by an interval corresponding to the taking-out and re-carrying of the boat or regulation of a process atmosphere.